1. Field of the Invention
This invention relates to a lighting apparatus and a liquid crystal display apparatus having the lighting apparatus.
2. Description of the Related Art
In recent years, liquid crystal display apparatuses used for car navigation systems and the like are required to have display property with high brightness. Such liquid crystal display apparatuses have a liquid crystal display panel and a back light unit. The liquid crystal display panel has an array substrate, an opposed substrate which is arranged opposed to the array substrate with a gap therebetween, and a liquid crystal layer held therebetween. The array substrate and the opposed substrate are adhered to each other by a sealing member provided on edge portions of the substrates.
The back light unit is provided on a back side of a display surface of the liquid crystal display panel, that is, on an external side of the array substrate. The back light unit has a light guiding plate including a light emission surface, and a light source arranged opposite to a side edge of the light guiding plate. Generally, a cathode-ray tube is used as the light source. Recently, light-emitting diodes (referred to as “LED” hereinafter) with high brightness have been developed, and an LED can be used as the light source.
A liquid crystal display device having a display screen with a size of 6 to 7 inches uses 20 or more LEDs to obtain display property with high brightness, and these LEDs are arranged along a side edge of the light guiding plate. An IC for driving an LED does not have a capacity to drive 20 LEDs connected in series. Therefore, as disclosed in Jpn. Pat. Appln. KOKAI Pub. No. 2001-76525, for example, LEDs are connected in parallel to form two or more circuits and driven. This enables a liquid crystal display apparatus to have display property with high brightness.
The above LEDs vary in brightness level due to error in manufacturing, and are classified into three types, that is, high-brightness LEDs, normal-brightness LEDs, and low-brightness LEDs. If the back light unit is formed by using LEDs having variations in brightness, a display image may have uneven brightness. Therefore, it is necessary to select LEDs having a brightness level of one of the above three types for the back light unit, to prevent unevenness in brightness.
However, if the back light unit is formed by using only LEDs having a brightness level of one type, use efficiency of the LEDs reduces since LEDs having brightness levels of the other two types are not used. Further, since the manufacturing cost of the LEDs is expensive, the price of the product rises.
The present invention has been made in view of the above. The object of the present invention is to provide a lighting apparatus and a liquid crystal display apparatus having the lighting apparatus, which can reduce the manufacturing cost and suppress unevenness in brightness.